Fluoropolymer is a polymer having fluorine atoms attached to the backbone of the polymer. Common fluoropolymers are polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene (ETFE) copolymers, tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) copolymers, and poly(vinylidine fluoride) (PVDF). Aqueous emulsion polymerization is known to be a particularly effective method to prepare such fluoropolymers. The emulsion polymerization process often requires the use of a fluorinated surfactant to stabilize the emulsion due to the high hydrophobicity of the monomer and the polymer formed. The fluorinated surfactant, such as perfluoroalkanoic acid or salt, is able to provide good dispersion stability, high polymerization yield, small particle sizes, and other desirable polymerization properties. However, this type of surfactant has increasingly become less favored due to the environmental concern and its high cost. An alternative method that can make use of more common surfactants is thus highly desirable.
Fluoropolymers are known to exhibit exceptional resistance to high temperature, chemicals, corrosion, and abrasion. They are capable of providing mechanical toughness, low friction, non-stick, and other properties desirable for high performance plastics, films, and coatings. Polystyrene is one of the most widely used plastics. Compared to aliphatic polymers, such as polyethylene and polypropylene, polystyrene is capable of providing unique mechanical and optical properties due to the presence of the hard, polarizable aromatic ring. However, polystyrene is inherently brittle, which has caused deficiencies in many of its applications. Thus, it is of particular interest to provide strong carbon-fluorine bonds to the backbone of polystyrene as a solution to solve this shortcoming and to obtain the unique properties exhibited by other fluoropolymers.
Fluoropolymers having a styrenic structure have not been widely studied due to the difficulty in preparing such monomers. Their polymerization methods have also rarely been investigated. Among various styrenic fluoropolymers, poly(α,β,β-trifluorostyrene) (PTFS) having the most fluorine atoms in the backbone is of particular interest. The preparation of PTFS disclosed in the prior art has been based on a study by Prober (J. of Amer. Chem. Soc., v. 75; 1953, p. 968-972). Prober teaches the preparation of PTFS by emulsion polymerization in the presence of a single surfactant using, respectively, Ivory® soap (yield, 67%), Aerosol OT (yield, 47%), or dodecylamine hydrochloride (yield, 83%). The method of using dodecylamine hydrochloride as the surfactant for the emulsion polymerization of α,β,β-trifluorostyrene (TFS) type of fluoromonomers has been further disclosed in U.S. Pat. Nos. 5,422,411 and 6,774,150.
It is known in the art that polymers produced from a polymerization process that results in low yields would have deficiencies in polymer properties such as molecular weight (MW) and glass transition temperature (Tg), which in turn would have detrimental effects on the mechanical and optical properties of the polymer films or coatings formed. In the application of fluoropolymers for high-performance films and coatings, it is particularly desirable to have a polymerization process that is capable of producing fluoropolymers in high yields due to the high cost of the fluoromonomer and the demand for high polymer quality. Thus, there exists a need for a polymerization process that is capable of producing fluoropolymers in high yields and with the desirable properties.